That looks very good, at least the part that is closest to the camera.
The only improvement I can think of is more turbulence.

> In particular, the reflections
> of the fur aren't calculated at all.

I don't think I understand what you mean. Reflective fur?

-- 
Martin Magnusson
Mar### [at] studentuuse
http://www.geocities.com/SoHo/9946/

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Martin Magnusson <Mar### [at] studentuuse> writes:
> 
> > In particular, the reflections
> > of the fur aren't calculated at all.
> 
> I don't think I understand what you mean. Reflective fur?

(Please excuse my bad English)
In the current picture, the lighting model isn't correct. Consider a 
point P on the surface of a hair. The normal vector of the hair at P 
is _not_ used to determine the amount of light that travels from a light 
source to the eye. At the moment, only the directions from P to the light
source and from P to the eye are used.

Furthermore, I would like to vary the colour of the fur. 

Simply speaking, I want to apply a texture to a media.

Thomas

-- 
http://www.fmi.uni-konstanz.de/~willhalm

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Thomas Willhalm wrote:
> 
> Martin Magnusson <Mar### [at] studentuuse> writes:
> >
> > > In particular, the reflections
> > > of the fur aren't calculated at all.
> >
> > I don't think I understand what you mean. Reflective fur?
> 
> (Please excuse my bad English)
> In the current picture, the lighting model isn't correct. Consider a
> point P on the surface of a hair. The normal vector of the hair at P
> is _not_ used to determine the amount of light that travels from a light
> source to the eye. At the moment, only the directions from P to the light
> source and from P to the eye are used.
> 
> Furthermore, I would like to vary the colour of the fur.
> 
> Simply speaking, I want to apply a texture to a media.
> 
> Thomas
> 
> --
> http://www.fmi.uni-konstanz.de/~willhalm

With my few tries at media I thought to my self how nice it would be
to use an image map applied to a media. It would look like holographic
projections on fog.

Your fur ball looks a lot like the teddy bear posted here during the
pov 3.1 beta testing period. It's appearence is very much like this.

-- 
Ken Tyler

mailto://tylereng@pacbell.net

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Thomas Willhalm wrote:
> 
> (Please excuse my bad English)
> In the current picture, the lighting model isn't correct. Consider a
> point P on the surface of a hair. The normal vector of the hair at P
> is _not_ used to determine the amount of light that travels from a light
> source to the eye. At the moment, only the directions from P to the light
> source and from P to the eye are used.
> 
> Furthermore, I would like to vary the colour of the fur.
> 
> Simply speaking, I want to apply a texture to a media.
> 
> Thomas
> 
> --
> http://www.fmi.uni-konstanz.de/~willhalm

I kind of doubt you can apply the phong (or whatever) lighting model to
media, since media does not have surface normals. It is a volume effect and
doesn't even have a surface as such. But perhaps you know better.
You should be able to apply a standard colour pattern (bozo etc) to your
fur, probably by using muliple medias in a container. I haven't experimented
much with this, though, so I can't be sure.
If you use the superpatch you _might_ achieve the fur effect with a
isosurface, since you have apparently developed a function that gives this
hairy appearance. If so, you wouldn't need to worry about applying lighting
models and textures.
Oh, and about your furball - it really does look like fur. A bit
transparent, but that should be easy to fix. Can it also make hair at
different angles? And how long does it take to render?

Margus

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Maybe you could simulate reflections with some emitting media here and
there?

just an idea,
ingo


Thomas Willhalm heeft geschreven in bericht ...
>Martin Magnusson <Mar### [at] studentuuse> writes:
>>
>> > In particular, the reflections
>> > of the fur aren't calculated at all.
>>
>> I don't think I understand what you mean. Reflective fur?
>
>(Please excuse my bad English)
>In the current picture, the lighting model isn't correct. Consider a
>point P on the surface of a hair. The normal vector of the hair at P
>is _not_ used to determine the amount of light that travels from a light
>source to the eye. At the moment, only the directions from P to the light
>source and from P to the eye are used.
>
>Furthermore, I would like to vary the colour of the fur.
>
>Simply speaking, I want to apply a texture to a media.
>
>Thomas
>
>--
>http://www.fmi.uni-konstanz.de/~willhalm

--
Met dank aan de muze met het glazen oog.

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Margus Ramst <mar### [at] peakeduee> writes:

> Thomas Willhalm wrote:
> > 
> > (Please excuse my bad English)
> > In the current picture, the lighting model isn't correct. Consider a
> > point P on the surface of a hair. The normal vector of the hair at P
> > is _not_ used to determine the amount of light that travels from a light
> > source to the eye. At the moment, only the directions from P to the light
> > source and from P to the eye are used.
> > 
> > Furthermore, I would like to vary the colour of the fur.
> > 
> > Simply speaking, I want to apply a texture to a media.
> > 
> 
> I kind of doubt you can apply the phong (or whatever) lighting model to
> media, since media does not have surface normals. It is a volume effect and
> doesn't even have a surface as such. But perhaps you know better.

As already mentioned, I try to implement the method described by Perlin
and Hoffert. They used the gradient of the density function to simulate
a surface normal. The images that they have in their paper look much
more realistic than my results so far.

> If you use the superpatch you _might_ achieve the fur effect with a
> isosurface, since you have apparently developed a function that gives this
> hairy appearance. If so, you wouldn't need to worry about applying lighting
> models and textures.

First, I want to point out that it's not "my" function, but the function
that is described in the paper. I have tried to use it as isosurface, but
the outcome wasn't very realistic. The clue with this function is that
it is used with partial transparent media. (At least, this is what I 
think now.)

> Oh, and about your furball - it really does look like fur. A bit
> transparent, but that should be easy to fix. Can it also make hair at
> different angles? 

I'm not totally sure about what you mean. You can't use this method 
to create single hairs that are next to each other but point in different
directions (or more precisely: I don't know how to do it). neighboured
hairs have to be almost parallel.

You can however add some turbulence to the function. This can result
in hairs that point in different direction at different regions of the
workpiece. Of course, you could also use a non-random function to
change the direction.

> And how long does it take to render?

Between 8 and 17 minutes with a "336 MHz SUNW,UltraSPARC-II" CPU.
The memory consumption is quite low. POV-Ray reports about 100 KB.

Thomas


-- 
http://www.fmi.uni-konstanz.de/~willhalm

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"ingo" <ing### [at] ingodemonnl> writes:

> Maybe you could simulate reflections with some emitting media here and
> there?

I have to modify the sources anyway. That's why I'm trying to implement
the reflections. It is probably not very complicated -- under the assumption
that I understand the existing code for medias.

Thomas

-- 
http://www.fmi.uni-konstanz.de/~willhalm

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Thomas Willhalm wrote:
/.../
> 
> You can however add some turbulence to the function. This can result
> in hairs that point in different direction at different regions of the
> workpiece. Of course, you could also use a non-random function to
> change the direction.

Yes, that's basically what I meant - hairs not pointing straight up from
the surface normal. Also, how controllable is the shape of these hairs -
can they be bent etc? I did a quick search, but I couldn't find the paper
you mentioned. Could you provide a link to it?

> 
> > And how long does it take to render?
> 
> Between 8 and 17 minutes with a "336 MHz SUNW,UltraSPARC-II" CPU.
> The memory consumption is quite low. POV-Ray reports about 100 KB.
> 

Well, I recently hit 450MB memory usage (250,000 objects - 50,000 hairs)
and a 2h/17h parse/render. So you most definitely have a superior method
in this respect.

Margus

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Margus Ramst <mar### [at] peakeduee> writes:

> Thomas Willhalm wrote:
> /.../
> > 
> > You can however add some turbulence to the function. This can result
> > in hairs that point in different direction at different regions of the
> > workpiece. Of course, you could also use a non-random function to
> > change the direction.
> 
> Yes, that's basically what I meant - hairs not pointing straight up from
> the surface normal. Also, how controllable is the shape of these hairs -
> can they be bent etc? I did a quick search, but I couldn't find the paper
> you mentioned. Could you provide a link to it?

As far as I know, the paper isn't available for free on the net. (The ACM
wants to earn some money.) You have to look for it in a library.

They model the fur like this:
You must provide a function R^3 -> R that is 1 at the surface of the object
and 0 at the top of the hairs. Then, the density function is roughly given
like this:
1. project the point to the surface
2. decide whether it is part of a hair by a noise function (The noise 
   function that is built in POV-Ray)
The values are adjusted by some functions to give a good ratio for empty
space and hairs. To incorporate reflections, they use the gradient to
simulate a normal.
You can modify the location of the point by a 3D noise function before
projecting it. That gives you some curly hairs.

I guess that it is also possible to include other modifications. It is
probably possible to simulate gravity and the like.

Thomas


-- 
http://www.fmi.uni-konstanz.de/~willhalm

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